A Building Stone Atlas of Leicestershire
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Strategic Stone Study A Building Stone Atlas of Leicestershire First published by English Heritage April 2012 Rebranded by Historic England December 2017 Introduction Leicestershire contains a wide range of distinctive building This is particularly true for the less common stone types. In stone lithologies and their areas of use show a close spatial some parts of the county showing considerable geological link to the underlying bedrock geology. variability, especially around Charnwood and in the north- west, a wide range of lithologies may be found in a single Charnwood Forest, located to the north-west of Leicester, building. Even the cobbles strewn across the land by the includes the county’s most dramatic scenery, with its rugged Pleistocene rivers and glaciers have occasionally been used tors, steep-sided valleys and scattered woodlands. The as wall facings and for paving, and frequently for infill and landscape is formed principally of ancient volcanic rocks, repair work. which include some of the oldest rocks found in England. To the west of Charnwood Forest, rocks of the Pennine Coal The county has few freestones, and has always relied on the Measures crop out around Ashby-de-la-Zouch, representing importation of such stone from adjacent counties (notably for the eastern edge of the Derbyshire-Leicestershire Coalfield. To use in the construction of its more prestigious buildings). Major the north-west of Charnwood lie the isolated outcrops of freestone quarries are found in neighbouring Derbyshire Breedon-on-the-Hill and Castle Donington, which are formed, (working Millstone Grit), Rutland and Lincolnshire (both respectively, of Carboniferous Limestone and Triassic working Lincolnshire Limestone), and in Northamptonshire (Bromsgrove) Sandstone. South of Charnwood Forest, a line (working Northampton Sand). Triassic Bromsgrove Sandstone can be drawn from Leicester to Lutterworth. To the west of this was extensively worked in some northern and western parts of line, the rocks that give rise to the gently undulating landscape the county, but additional stone may have come from are almost all of Triassic age, and comprise sandstones and Warwickshire and Staffordshire. The only other freestone red mudstones deposited in fluvial and semi-arid desert occurs in the east – the ochreous brown ‘ironstones’ of the environments. To the east, meanwhile, marine sedimentary Middle Lias (mid-to-upper Lower Jurassic), used in abundance rocks of Jurassic age crop out, the erosion of which has formed in local vernacular architecture. ridge and vale scenery, with limestones and ironstones capping the hills and softer mudstones cropping out in the There are no active building stone quarries in Leicestershire, valley floors. and the county has never been a net exporter of building stone. The county’s hard igneous rocks are a noteworthy During the early Pleistocene, around 2 million years ago, exception, however, these being supplied mainly for modern day Leicestershire lay within the drainage basin of a kerbstones and paving setts – and also a minor amount of major river system – the Bytham River – which flowed building stone – from the early 19th century. Today, four eastwards to Norfolk and out into the present North Sea area. quarries continue to supply aggregate for use throughout By the middle Pleistocene, glaciers advanced and retreated southern Britain, and one of them (Buddon Wood Quarry) will over the whole county, depositing sands and gravels, still provide small quantities for building and decorative use. laminated clays and unsorted till, forming a blanket over the older rocks. New river channels later cut through these The diversity of Leicestershire’s building stone heritage is unconsolidated glacial deposits, locally exposing the older reflected in its Roman architecture. Leicester was an important harder rocks, and ultimately giving rise to the distinct Roman town, and has one of the finest surviving Roman topographic features we see today. structures in Britain - the Jewry Wall. Decoratively built of courses of thin, locally-made Roman clay bricks and at least As noted at the outset, there is a close relationship between eight types of locally sourced rubblestone, it is an architectural the local geology and the selection of building materials. catalogue of the local stone resources. Generally, stone has been used close to its source, especially in the case of older buildings. XXX Strategic Stone Study 1 Leicestershire Bedrock Geology Map Derived from BGS digital geological mapping at 1:625,000 scale, British Geological Survey ©NERC. All rights reserved Leicestershire Strategic Stone Study 2 Precambrian (Neoproterozoic) Lavas & Lava-Breccias Charnian Supergroup The volcanoes that formed the rocks of Charnwood are thought to have had their magmatic centre close to the Charnwood Forest is an area of craggy hills, about 10 km wide, present day Bardon Hill in the west of the forest. There are two located to the north-west of Leicester. Its relatively small associated volcanic complexes, each now the site of a large outcrops represent the exhumed topography of an ancient quarries, at Bardon and Whitwick. The lavas are of andesitic or mountain range, the lower slopes of which remain buried dacitic composition, and have been quarried primarily to beneath the Triassic strata that now surround it. The rocks are supply aggregate to the south and east of England. This largely the products of explosive volcanic eruptions, and practice has been going on for well over a century, but these include lavas, volcanic breccias, conglomerates and tuffs. rocks have also been used locally as a building stone (albeit to Several igneous intrusions are also present. They were formed a limited extent) for much longer. between about 650 and 540 million years ago, and have been divided into three major stratigraphical units: the Blackbrook, Bardon Hill Volcanic Complex Maplewell and Brand groups. These collectively make up the Charnian Supergroup. Bardon Breccia This is best observed in the ornate 19th-century Bardon The older buildings, especially the medieval churches, tend to church, where it has been used as an angular rubblestone, include a wide variety of Charnian rock types. There are few (with Lincolnshire Limestone dressings), known to the pre-Victorian buildings in the centre of Charnwood, as the quarrymen as the ‘good-rock’. It is a dark green-grey, fine- Forest was originally a hunting reserve dating back to grained stone (andesite) that is indistinctly mottled in parts medieval times. With the exception of Ulverscroft Priory, all the (owing to its brecciated state). Staining of the joint surfaces, medieval churches and other structures are located on the gives the occasional block a dull dark red colour. Bardon periphery of the park. Only the Victorian and later churches Breccia is the building stone used at Bardon Church (below). tend to display a single stone type in their wall fabrics. The Charnian rocks are very hard and are almost invariably used in buildings and walls as uncoursed, angular rubblestone. All of them are cleaved to some extent. The cleavage and joint planes determine the shape of the blocks, and these surfaces often weather to shades of red, brown or cream, quite different from the common greys and greens of the fresh stone. A single wall can, consequently, appear to be composed of several different stone types when it is actually built of just one or two with varying degrees of weathering. When used as building stone, the ‘magmatic lithologies’ (lavas and intrusive rocks) are easier to identify than most of the varied fragmental volcaniclastic lithologies of the Charnian sequence. For this reason, the ‘magmatic’ stones have been named and described individually, while the volcaniclastic stones have been grouped by lithological type. Bardon Church. Leicestershire Strategic Stone Study 3 The Old Covent in Whitwick is built of Grimley Andesite. Whitwick Volcanic Complex Grimley Andesite This andesitic lava occurs as a massive, weakly cleaved rock in and around Whitwick, and is exposed in small quarries in the centre of the village. The nature of the stone can be more easily examined at the Old Convent in Whitwick. Some enormous blocks have been used in the walls. The stone is very hard and fine-grained, and it commonly weathers to a strong red colour, although it may be mottled with the original dark grey-green shades still visible. It is used as rubblestone, in association with other local Charnian rocks, in building and Peldar Dacite Breccia in the walls boundary walls up to four kilometres away from its outcrop. of Mount St Bernard Abbey. Peldar Dacite Breccia Weathered surfaces can appear uneven, showing a corrugated The large quarry at Whitwick, west of the village, is the source texture. Joint surfaces often weather to a cream or rusty brown of two distinctive stones: Peldar Dacite Breccia and Sharpley colour. Both stones have been used with other local stones Porphyritic Dacite. The former is a dark grey to greenish grey, across north-west Charnwood. Peldar Dacite Breccia is fine-grained lava enclosing ‘blobs’ of very similar coarser- conspicuous in the lower stage of the tower at Osgathorpe grained lava with large crystals (phenocrysts) of quartz and church, and is also seen in nearby houses (up to several cloudy grey feldspar. The quartz crystals are unusually dark kilometres from Whitwick). It is also one of the stones used in and full of fractures. the walls of Mount St Bernard Abbey (above). Leicestershire Strategic Stone Study 4 Charnian volcaniclastic sandstone is used in Blackbrook Farmhouse. Sharpley Porphyritic Dacite Blackbrook Group This is best seen in the walls of Belton church. It is a fine- grained, pale grey to pale purple stone with large (up to 5 mm) ‘Charnian volcaniclastic sandstone’ phenocrysts of grey transparent quartz and cloudy grey The oldest volcaniclastic rocks crop out in central and north- feldspar. The distinctive features of this stone are the purple west Charnwood.